Polyolefins, e.g., polyethylene and polypropylene, are excellent in a mechanical property, a chemical resisting property and extremely excellent in the balance of these properties and economical efficiency, therefore, widely used in a variety of fields for various purposes as polymer materials having extremely high practicality.
These polyolefins have been conventionally manufactured as polyolefins excellent in various physical properties and stereoregularity by polymerizing olefin with so-called Ziegler-Natta catalysts comprising combination of mainly titanium trichloride, titanium tetrachloride, or transition metal catalysts carrying these on a carrier, e.g., magnesium chloride, with organoaluminum compounds. And improvement has been continued in catalytic activity and stereoregularity by using various kinds of carriers, electron donors and organosilane compounds.
Contrary to this, manufacturing methods of polyolefin by polymerizing olefin with so-called metallocene catalysts which are single site catalysts comprising transition metal complexes comprising metal atoms coordinated with cyclopentadienyl ring etc. in combination with cocatalysts such as aluminoxane, different from Ziegler-Natta catalysts which are multi-site catalysts, have been developed and these methods recently attract public attention rather than the polymerization methods by Ziegler-Natta catalysts.
This is because metallocene catalysts are soluble in organic solvents and make it possible to perform homogeneous polymerization, they have very high catalytic activity, they can bring about specific stereoregularities, and high molecular weight polyolefins having a narrow molecular weight distribution can be manufactured, and so the improvement and development in the ligands, substituents thereof, transition metals, cocatalysts and supports have been continued. In addition, the development of cocatalysts other than expensive aluminoxane and third components, e.g., organoaluminum compounds are now continued. Metallocene catalysts also make it possible to polymerize higher olefins, cyclic olefins and polar monomers.
As described above, metallocene catalysts are generally recognized as epoch-making, very excellent and important catalysts in the polymerization of polyolefin, however, metallocene catalysts have many problems to be solved, such as the application to heterogeneous reaction such as slurry polymerization, the development of the substitutes of expensive aluminoxane, and the reduction of sensitive catalytic activity due to impurities. In particular, metallocene catalysts are more sensitive to impurities in a polymerization reaction system as compared with Ziegler-Natta catalysts, accordingly strict control and management of materials such as monomers and catalysts and impurities in polymerization reaction are required, which has been a bottleneck in the way of large-scale and efficient industrialization of olefin polymerization by metallocene catalysts.
A variety of proposals for improvement have been done for the purpose of improving these problems in the industrialization of metallocene catalysts. For example, as the application to heterogeneous reaction, a proposal to use silica-supported methylaluminoxane (refer to patent literature 1), a proposal to use non-coordinate boron compounds of Lewis acid as the substitute for expensive aluminoxane (refer to patent literature 2 and 3), and a proposal to use ion exchange layered silicate (refer to patent literature 4 and 5) are disclosed.
Further, for increasing polymerization efficiency by excluding impurities, the improving means of materials have been supposed in large numbers in recent years, and for refining the solvents after polymerization reaction for reuse, e.g., a method of bringing the solvent to be reused into contact with an adsorbent and removing the components originated from the metallocene compound by adsorption is disclosed (refer to patent literature 6). For removing impurities from catalyst components, there are disclosed a refining method by washing a metallocene compound containing ether compound impurities with a halogenated hydrocarbon solvent (refer to patent literature 7), a method of differentially refining transition metal-aromatic compounds containing impurities by liquid chromatography packed with porous carbon (refer to patent literature 8), and to improve the quality of metallocene catalysts, a method of separating inorganic impurities such as metal halide by using organic solvents and removing organic impurities by granulated adsorbing materials (refer to patent literature 9), and to refine feedstock gas to be reused, a method of preventing the reduction of activity of metallocene catalysts by removing impurities by passing unreacted gas after polymerization reaction through fixed bed adsorption column (refer to patent literature 10).
In addition, for increasing polymerization efficiency by removing impurities, although specific impurities are not exemplified, it is also disclosed to use organoaluminum compounds as the scavenger to remove impurities (refer to patent literature 11 and 12). Triethylaluminum and triisobutylaluminum are mainly used as the organoaluminum of scavengers which are the antidotes of catalysts. In addition, in this case, it was conventionally thought that every catalyst poison could be removed by the above organoaluminum. However, as described later, it was unexpectedly found from the close examination by the present inventors that halogen-containing compounds become strong catalyst poisons to metallocene catalysts.
And in any of the above methods, it seems that impurities are not sufficiently detoxified or removed, and catalytic activity and polymerization efficiency are not completely satisfied. Further, methods of specifying the catalyst poisons of metallocene catalysts and adopting effective means against them have not been realized yet.
As described above, metallocene catalysts are more sensitive to impurities in the system of polymerization reaction as compared with Ziegler-Natta catalysts, therefore, strict control and management of materials such as monomers and catalysts and impurities in polymerization reaction are required, which problems have been bottlenecks in the way of large-scale and efficient industrialization of olefin polymerization by metallocene catalysts, and recognized as the main problem to be solved.
[Patent literature 1]: JP-A-6-206924 (claim 1, paragraphs 0013 and 0063) (the term “JP-A” as used herein means an “unexamined published Japanese patent application”).
[Patent literature 2]: JP-A-3-234709 (claim 1).
[Patent literature 3]: JP-A-5-247128 (paragraph 0024).
[Patent literature 4]: JP-A-11-49812 (claim 1).
[Patent literature 5]: JP-A-11-140112 (claim 1).
[Patent literature 6]: JP-A-2001-62202 (claim 1).
[Patent literature 7]: JP-A-7-97388 (claim 1).
[Patent literature 8]: JP-A-9-47602 (claim 1).
[Patent literature 9]: JP-T-11-510545 (abstract, claim 1) (the term “JP-T” as used herein means a published Japanese translation of a PCT patent application).
[Patent literature 10]: JP-A-8-3226 (claim 1).
[Patent literature 11]: JP-A-5-140227 (paragraph 0061).
[Patent literature 12]: JP-A-11-60623 (paragraph 0009).
In the state of problems in metallocene catalysts, it is thought to be novel and important objects to increase catalytic activity and polymerization efficiency by the accurate control of materials such as monomers and catalysts or solvents and impurities in polymerization reaction systems, to sufficiently bring out the performances of metallocene catalysts and maintain stable polymerization reaction, to thereby embody large-scale and efficient industrialization of olefin polymerization by metallocene catalysts.
These problems are recognized to be important in olefin polymerization by metallocene catalysts, however, in the past, only attention was paid to the removal of unspecified impurities in individual material such as catalyst, solvent etc., and it was hardly known to synthetically and accurately control impurities by grasping both material systems and polymerization reaction systems.
The present invention aims at solving these new problems and bringing out the performances of metallocene catalysts and maintaining stable polymerization reaction, to thereby embody large-scale and efficient industrialization of olefin polymerization by metallocene catalysts. That is, the object of the present invention is to provide a manufacturing method of polyolefin capable of maintaining stable production by sufficiently bringing out the performances of catalysts under the conditions not influenced by the catalyst poisons of impurities.